The present invention relates to a golf club head.
Generally, there has been known a golf club head in which a weight body is disposed in the interior of a hollow head in order to improve the directionality of a golf ball hit by the head. For example, in Patent Document 1, a golf club head is disclosed in which a weight body is placed at a position located at the rear of a crown portion and close to the axis of a club shaft in order to set the angle of the center of gravity of the head within a predetermined range (30.5 to 35 degrees). According to the golf club head like this, since a face side is made to rotate easily about the axis of the club shaft when a golf club is swung, the head is also made to easily turn, thereby making it possible to obtain an effect to prevent a slice shot. In addition, in Patent Document 2, a golf club head is disclosed in which a weight body is placed on a face side in the vicinity of a sweet spot. According to the golf club head like this, the player can sense the position of the sweet spot and the orientation of the clubface due to the concentration of the weight component on a single specific point on the head when swinging a golf club, thereby making it possible to obtain an effect to enable the player to easily hit the ball at a position close to the sweet spot.
Incidentally, as shown in FIG. 1, a swing of the golf club is made up of backswing from “the address” or setup (paths indicated by arrows A, B) to “the top of swing”, the downswing (a path indicated by an arrow C) through the release of the cock of the wrists to the impact (a path indicated by arrow D), the follow through and the finish in this order. In this series of stages, during the backswing from the address, the clubface faces the front of the player as the grip of the club reaches the vicinity of the waist of the player, and during the stage of the downswing from the top, the clubface remains facing the front of the player until the grip returns to the vicinity of the waist of the player. Then, during the stage in which the grip moves from the vicinity of the waist of the player to the impact point, the so-called release of the cock of the wrists, the clubface is made to stay square to the path of the head in the downswing for impact. Namely, as shown in FIG. 2, in the path indicated by the arrow D, the player operates the club in such a manner as to rotate about the shaft axis X during the downswing thereof along a swing plane SP, so that the clubface becomes square to the ball at impact.
Thus, while the orientation of the head during the stage of releasing the cock of the wrists becomes vital with a view to eventually directing the clubface square to the target line of the ball at impact, an inertial force is exerted on the head during the swing, and in particular, with the aforesaid head construction according to the related art, since the weight body is concentrated at the single point (or is caused to reside at the single point), an inertial force is generated inherently by the weight body which resides at the single point.
While the aforesaid related techniques are such a technique that the orientation of the clubface is modified during the series of stages of the swing, no consideration is taken into on the inertial force so exerted on the head when the cock of the wrists is released. Namely, the inertial force generated by the weight component which resides at the single point needs to be dealt with by adding a certain force, and in the path indicated by the arrow D, the player needs to modify the orientation of the clubface in such a manner as to coincide with the direction of the swing plane through an operation of by, for example, twisting the wrists of the player, so that the clubface is eventually aligned squarely with the ball. Thus, with the related techniques, there is caused a problem that the techniques are inferior in an aspect of orienting the clubface square to the ball. As a result, in the related techniques, the swing tends to be easily destabilized during the path indicated by the arrow D due to the operation for controlling the inertial force generated by the weight component which is caused to reside at the single point in the head, and a certain swing technique is required to cope with the inertial force so generated so as to orient the clubface square to the ball, thus leading to a problem that the related techniques are inferior with respect to the stability (accuracy) of the direction of the ball hit.
In addition, in the golf club heads, it is generally known that the improvement in driving distance of a ball can be realized by reducing the loss of energy generated at impact by, in turn, making the deflection of the clubface coincide with the deformation of the ball at impact. For example, the deflection of the clubface at impact can be facilitated by making the clubface thinner, or the deflection of the clubface at impact can be facilitated by changing the thickness of the clubface (increasing the thickness of the ball hitting area, while decreasing the thickness of the peripheral area thereof).
In the case that the thickness of the clubface is decreased or changed, however, there is caused a problem that the clubface becomes easier to be damaged as the thickness thereof is decreased or changed.
Due to this, in Patent Document 3, there is disclosed a golf club head in which a material having a lower rigidity than that of a material used for a sole portion is used for a crown portion of a head body, so that the crown portion is deflected at impact so as to increase the driving distance. In addition, Patent Document 4 discloses a golf club head in which an opening is formed in a crown portion of a head body, so that a fiber-reinforced resin plate is fitted in the opening in such a manner as to make up the crown portion. In this construction, since the fiber-reinforced resin plate has a high specific strength, the center of gravity of the head can be lowered, which is effective in reducing the spin of the ball and increasing the angle of trajectory of the ball hit, thereby making it possible to increase the driving distance.
Since the golf club head disclosed in Patent Document 3 is constructed such that the whole of the crown portion is deflected, the energy generated at impact is transmitted to the rear of the crown portion in association with the deflection, and hence the energy is lost, whereby the properties of reaction become difficult to be improved, leading to a problem that the driving distance cannot be improved sufficiently. In addition, while the golf club head disclosed in Patent Document 4 can realize the lowering of the center of gravity by using the fiber-reinforced resin plate having the high specific strength, as with the construction disclosed in Patent Document 1, since the entirety of the crown portion is deflected, the loss of energy is caused, leading to the problem that the driving distance cannot be improved sufficiently. Furthermore, there is caused another problem that due to too small the hitting sound and too soft the hitting feeling, a hitting error becomes difficult to be sensed by the player.
Additionally, adjusting the weight of the head in the golf club head is generally known. For example, in Patent Document 5, there is disclosed a golf club head in which a nut which functions as a rough adjustment weight for roughly adjusting the weight of the head and a fine adjustment weight which is adapted to be screwed into a screw hole provided in a bolt adapted to be screwed into the nut are provided in a sole portion of a head body. Then, the swing weight is made to be adjusted by cutting part of the nut or selecting appropriate nut and weight from pluralities of nuts and fine adjustment weights prepared in advance which differ from one another in weight.
In addition, Patent Document 6 discloses a golf club head in which a weight is fixed to a sole portion while being exposed therefrom, so that an exposed portion of the weight is abraded for adjusting the weight of a head body.
The golf club head disclosed in Patent Document 5 is formed so as to adopt the technique to adjust the overall weight of the head and however has a problem that the position of the center of gravity thereof is difficult to be adjusted (a slight vertical weight adjustment is possible). In addition, as to the golf club head disclosed in Patent Document 6, while the overall weight of the head can be adjusted, the position of the center of gravity thereof is difficult to be adjusted, and there is possibly caused a risk that the external shape is changed depending upon the amount of abrasion, whereby the external appearance is defaced.
Namely, in manufacturing golf club heads, when the weight of a head becomes heavier than a designed weight, when the head needs to be re-adjusted after the completion of weight adjustment, or when the position of the center of gravity of the head needs to be adjusted finely in the toe-to-heel or face-to-back direction as well as the vertical direction, with the aforesaid related techniques, it is difficult to carry out the needed adjustments with ease and good accuracy.    Patent Document 1: JP-A-2002-113135    Patent Document 2: JP-A-2002-219199    Patent Document 3: JP-B-7-98076    Patent Document 4: JP-A-2003-111874    Patent Document 5: JP-A-62-72670U    Patent Document 6: JP-A-2001-204858